506
FXUS02 KWBC 121940
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
339 PM EDT MON JUN 12 2023
VALID 12Z THU JUN 15 2023 - 12Z MON JUN 19 2023
...EARLY SEASON HEATWAVE TO PERSIST ACROSS MUCH OF THE
SOUTH-CENTRAL U.S. INTO EARLY NEXT WEEK AND BEYOND...
..SYNOPTIC OVERVIEW
A WEAK OMEGA BLOCK PATTERN ACROSS SOUTHERN CANADA AND THE NORTHERN
TIER OF THE U.S. IS EXPECTED TO BE IN PLACE FOR THE MIDDLE TO END
OF THIS WEEK, WITH A BROAD UPPER LOW SITUATED OVER SOUTHERN
QUEBEC, A RIDGE ACROSS MANITOBA, AND A TROUGH OVER SOUTHWESTERN
CANADA AND INTO MONTANA. THIS BREAKS DOWN SOME GOING INTO NEXT
WEEKEND WITH THE RIDGE DECAYING DOWN AND MORE OF A QUASI-ZONAL
FLOW PATTERN DEVELOPS ACROSS THE CENTRAL STATES. A STRONGER
TROUGH BEGINS TO BUILD SOUTHWARD ACROSS THE PACIFIC NORTHWEST AND
INTO THE NORTHERN ROCKIES BY SUNDAY AND NEXT MONDAY. MEANWHILE,
THE UPPER RIDGE OVER TEXAS AND THE WESTERN GULF OF MEXICO WILL
CONTINUE WITH THE ONGOING HEATWAVE UNABATED THROUGH THE FORECAST
PERIOD (AND BEYOND PER THE LATEST FROM THE CLIMATE PREDICTION
CENTER), WHILE ANOTHER TROUGH AND SURFACE LOW WILL LIKELY DEVELOP
ACROSS THE EAST COAST REGION BY SUNDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW OVERALL GOOD SYNOPTIC-SCALE
AGREEMENT THROUGH THE PERIOD FOR THE UPPER PATTERN, BUT SOME
VARIABILITY IN THE DETAILS. THE GREATEST MODEL DIFFERENCES
CONTINUE WITH SOME WEAK SHORTWAVE ENERGY CROSSING FROM THIS UPPER
MIDWEST TO THE OHIO VALLEY THIS WEEKEND, ADDING TO UNCERTAINTIES
IN THE RAINFALL FORECAST ACROSS THESE REGIONS AS WELL. THERE ARE
HINTS OF SOME SORT OF COMPACT UPPER LOW CROSSING INTO THE EAST
EARLY NEXT WEEK BUT PLENTY OF RUN TO RUN VARIABILITY ON ANY SORT
OF FEATURE. THERE IS ALSO TIMING UNCERTAINTIES OF WAVES CROSSING
THE NORTHEAST AHEAD OF THE AFOREMENTIONED FEATURE, AND ALSO
PLACEMENT OF A DEEPER UPPER LOW IN SOUTHWEST CANADA OR THE PACIFIC
NORTHWEST AT THE END OF THE PERIOD. MOST OF THESE DIFFERENCES ARE
SMALLER IN SCALE AND MAY TAKE UNTIL THE SHORT RANGE PERIOD TO
FULLY RESOLVE. A GENERAL MODEL BLEND OF THE DETERMINISTIC MODELS
WORKED WELL FOR THE FIRST HALF OF THE PERIOD, BUT THE LATTER DAYS
TRANSITIONED TOWARDS THE ENSEMBLE MEANS, WITH SOME CONTRIBUTIONS
FROM THE DETERMINISTIC ECMWF AND GFS JUST FOR A LITTLE ADDED
SYSTEM DEFINITION. THIS APPROACH FIT WELL WITH PREVIOUS SHIFT WPC
CONTINUITY AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAIN FOCUS FOR HEAVY RAINFALL IS EXPECTED ACROSS PORTIONS OF
THE DEEP SOUTH/SOUTHEAST MID-LATE WEEK ALONG A LINGERING FRONT,
WHERE AN AXIS OF 1-2 INCH RAINFALL TOTALS WITH ISOLATED HIGHER
AMOUNTS IS EXPECTED, MAINLY FROM THE FLORIDA PANHANDLE TO SOUTHERN
GEORGIA. MOST OF THE SHOWERS AND STORMS THAT DEVELOP WILL BE SOUTH
OF THE WARM FRONT AND REACH PEAK INTENSITY DURING THE AFTERNOON
HOURS, AND SOME STORMS MAY BE STRONG ENOUGH TO PRODUCE INSTANCES
OF FLOODING. HOWEVER, THE COVERAGE OF THIS SHOULD BE FAIRLY
ISOLATED IN MOST CASES, SO THIS ONLY WARRANTS A MARGINAL RISK AREA
ON THE DAY 4 EXCESSIVE RAINFALL OUTLOOK AT THIS TIME. ADDITIONAL
HEAVY RAINFALL MAY ALSO AFFECT THE SOUTHEAST U.S. GOING INTO
SUNDAY AND MONDAY AS THE NEXT SYNOPTIC SCALE DISTURBANCE
APPROACHES. ANOTHER AREA TO MONITOR FOR HEAVY RAINFALL POTENTIAL
WILL BE ACROSS THE CENTRAL PLAINS AND EXTENDING INTO THE UPPER
MIDWEST WHERE A FEW MESOSCALE CONVECTIVE SYSTEMS WILL BE POSSIBLE
AHEAD OF A FRONTAL BOUNDARY THAT WILL INTERCEPT INCREASING
MOISTURE ADVECTION, AND A MARGINAL RISK AREA FOR EXCESSIVE
RAINFALL IS IN EFFECT FOR THIS REGION AS WELL. ELSEWHERE, SOME
SHOWERS ARE LIKELY FROM THE GREAT LAKES TO THE NORTHEAST AS
MOISTURE PIVOTS AROUND THE UPPER LEVEL LOW.
THE EXCESSIVE HEAT CONTINUES GOING THROUGH THIS WEEKEND (AND
BEYOND) ACROSS MUCH OF TEXAS AND INTO LOUISIANA AND OKLAHOMA, WITH
WIDESPREAD 100S ACROSS CENTRAL AND SOUTHERN PORTIONS OF TEXAS.
RECORD TEMPERATURES AND HEAT INDICES ON THE ORDER OF 105 TO 115
DEGREES ARE LIKELY DURING THE HOTTEST PARTS OF THE DAY FOR MANY OF
THESE AREAS, AND SOME ISOLATED INSTANCES OF HEAT INDICES UP TO 120
DEGREES ARE POSSIBLE FOR PARTS OF DEEP SOUTH TEXAS WHERE THE
GREATEST COMBINATION OF HIGH DEWPOINTS AND THE HEAT WILL LIKELY
EXIST. AS PER THE LATEST FORECAST FROM THE CLIMATE PREDICTION
CENTER, THIS HEAT SHOULD PERSIST BEYOND DAY 7 AS WELL. IT WILL
ALSO BE QUITE WARM ACROSS THE NORTHERN PLAINS/UPPER MIDWEST STATES
TO CLOSE OUT THE WEEK WITH WIDESPREAD UPPER 80S AND LOWER 90S
EXPECTED BEFORE A MODEST COOL DOWN ARRIVES BY SATURDAY, AND THEN
ANOTHER WARM-UP LIKELY ENSUES BY SUNDAY AND INTO MONDAY. THE
BUILDING UPPER TROUGH ACROSS THE NORTHWEST U.S. WILL HERALD THE
ARRIVAL OF COOLER TEMPERATURES BY SUNDAY FROM CALIFORNIA TO
WASHINGTON STATE, WITH HIGHS GENERALLY AS MUCH AS 10 DEGREES BELOW
AVERAGE BY MONDAY. MOST OF THE EAST COAST REGION SHOULD BE NEAR
CLIMATOLOGICAL MID-JUNE LEVELS.
SANTORELLI/HAMRICK
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE CENTRAL
GREAT BASIN, THE NORTHERN PLAINS,
THE TENNESSEE VALLEY, THE CENTRAL ROCKIES, THE SOUTHERN
APPALACHIANS, AND THE SOUTHEAST, THU, JUN
15.
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE UPPER
MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS, FRI, JUN 16.
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE
TENNESSEE VALLEY, THE MIDDLE
MISSISSIPPI VALLEY, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, THE
GREAT LAKES, AND THE OHIO VALLEY,
SAT, JUN 17.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE
CENTRAL PLAINS, AND THE NORTHERN
PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN
ROCKIES AND THE NORTHERN GREAT
BASIN.
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, THE
NORTHERN ROCKIES, THE NORTHERN
GREAT BASIN, AND THE NORTHERN PLAINS.
- EXCESSIVE HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY
AND THE SOUTHERN PLAINS, THU-MON,
JUN 15-JUN 19.
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
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